A projection system is widely used in our daily lives to project texts/pictures or image data onto a screen in order to facilitate many people to view the enlarged texts/pictures or image data in a visually comfortable manner. Recently, the general trends in designing electronic devices are toward small size, light weightiness and easy portability to meet the requirements of humanization. Similarly, the projection system is developed toward miniaturization. As a consequence, the projection system can be applied to electronic devices such as 3G mobile phones or personal digital assistants (PDAs). In addition, a small-sized projection system becomes a portable electronic device. On account of its portability, the user may use a small-sized projection system to watch movies everywhere they are, and thus the amusement purpose can be achieved without difficulty.
FIG. 1 is a schematic view illustrating the structure and the optical paths of a conventional LCOS projection system. As shown in FIG. 1, the LCOS projection system 1 comprises an illumination device 11, a collimating lens assembly 12, a front-end polarizer 17, a polarization beam splitter (PBS) 13, a field lens 14, a LCOS microdisplay element 15, and an optical projection lens 16. The polarization beam splitter 13 comprises two prisms, wherein a reflective polarizing film 131 is formed on the interface between these two prisms. The polarization beam splitter 13 is arranged between the illumination device 11, the LCOS microdisplay element 15 and the optical projection lens 16. The collimating lens assembly 12 is arranged between the illumination device 11 and the front-end polarizer 17. The field lens 14 is arranged between the LCOS microdisplay element 15 and the polarization beam splitter 13.
The collimating lens assembly 12 and the field lens 14 are used for adjusting the incidence angles of the received light beams and outputting the adjusted light beams. The front-end polarizer 17 is used for blocking the P-polarized beams because the P-polarized beams are reflected or absorbed by the front-end polarizer 17. In addition, only the S-polarized beams are transmissible through the front-end polarizer 17. On the other hand, the reflective polarizing film 131 of the polarization beam splitter 13 is used for blocking the S-polarized beams because the S-polarized beams are reflected by the reflective polarizing film 131. In addition, only the P-polarized beams are transmissible through the reflective polarizing film 131 of the polarization beam splitter 13.
Moreover, the LCOS microdisplay element 15 is used for showing an electronic image. The illumination device 11 is used for providing a source ray to the LCOS microdisplay element 15. Consequently, a plurality of lighting paths are created between the illumination device 11 and the LCOS microdisplay element 15, and a plurality of imaging paths are created between the LCOS microdisplay element 15 and the optical projection lens 16. The electronic image is then projected onto a screen 9 through the optical projection lens 16.
Please refer to FIG. 1 again. The source ray provided by the illumination device 11 may be divided into two parts, i.e. P-polarized lighting beams LIP and S-polarized lighting beams L1S. The P-polarized lighting beams LIP and the S-polarized lighting beams L1S are propagated along the corresponding lighting paths. The solid lines as shown in FIG. 1 denote some of the lighting paths, i.e. the transmission paths of the lighting beams (L1P+L1S).
After the source ray (L1P+L1S) provided by the illumination device 11 is transmitted through the collimating lens assembly 12 and directed to the front-end polarizer 17, the S-polarized lighting beams L1S are transmitted through the front-end polarizer 17 and directed to the polarization beam splitter 13. Whereas, the P-polarized lighting beams LIP are reflected to other places (not shown). Next, the S-polarized lighting beams L1S are reflected by the reflective polarizing film 131 of the polarization beam splitter 13, and directed to the LCOS microdisplay element 15 through the field lens 14. Next, the S-polarized lighting beams L1S are reflected by the LCOS microdisplay element 15. Correspondingly, the S-polarized lighting beams L1S are converted into a plurality of P-polarized imaging beams I1P in response to the electronic image. The P-polarized imaging beams I1P are propagated along the corresponding imaging paths. The dotted lines as shown in FIG. 1 denote some of the imaging paths, i.e. the transmission paths of the P-polarized imaging beams I1P.
The P-polarized imaging beams I1P from the LCOS microdisplay element 15 are transmitted through the field lens 14, and directed to the polarization beam splitter 13. Next, the P-polarized imaging beams I1P are transmitted through the reflective polarizing film 131 of the polarization beam splitter 13, and directed to the optical projection lens 16. Consequently, the electronic image shown on the LCOS microdisplay element 15 is projected onto the screen 9 through the optical projection lens 16.
From the above discussions, the S-polarized lighting beams L1S are reflected by the reflective polarizing film 131 of the polarization beam splitter 13, and the P-polarized imaging beams I1P are transmissible through the reflective polarizing film 131 of the polarization beam splitter 13. However, the reflectivity and the transmissivity of the reflective polarizing film 131 are not ideally 100%. In other words, a portion of the S-polarized lighting beams L1S incident to the reflective polarizing film 131 are reflected by the reflective polarizing film 131 and directed to the LCOS microdisplay element 15. Whereas, the rest of the S-polarized lighting beams L1S are consumed or lost. In addition, a portion of the P-polarized imaging beams I1P incident to the reflective polarizing film 131 are transmitted through the reflective polarizing film 131 and directed to the optical projection lens 16. Whereas, the rest of the P-polarized imaging beams I1P are consumed or lost. That is, the light amount outputted from the optical projection lens 16 is much lower than the light amount outputted from the illumination device 11.
FIG. 2 is a schematic view illustrating the structure and the optical paths of another conventional LCOS projection system. As shown in FIG. 2, the LCOS projection system 2 comprises an illumination device 21, a collimating lens assembly 22, a reflective polarizer 23, a field lens 24, a LCOS microdisplay element 25, an analyzer 28, and an optical projection lens 26. The reflective polarizer 23 is arranged between the illumination device 21, the LCOS microdisplay element 25 and the optical projection lens 26. The collimating lens assembly 22 is arranged between the illumination device 21 and the reflective polarizer 23. The field lens 24 is arranged between the LCOS microdisplay element 25 and the reflective polarizer 23.
The collimating lens assembly 22 and the field lens 24 are used for adjusting the incidence angles of the received light beams and outputting the adjusted light beams. The reflective polarizer 23 is used for blocking the S-polarized beams because the S-polarized beams are reflected by the reflective polarizer 23. In addition, only the P-polarized beams are transmissible through the reflective polarizer 23.
Moreover, the LCOS microdisplay element 25 is used for showing an electronic image. The illumination device 21 is used for providing a source ray to the LCOS microdisplay element 25. Consequently, a plurality of lighting paths are created between the illumination device 21 and the LCOS microdisplay element 25, and a plurality of imaging paths are created between the LCOS microdisplay element 25 and the optical projection lens 26. The electronic image is then projected onto a screen 9 through the optical projection lens 26.
Please refer to FIG. 2 again. The source ray provided by the illumination device 21 may be divided into two parts, i.e. P-polarized lighting beams L2P and S-polarized lighting beams L2P. The P-polarized lighting beams L2P and the S-polarized lighting beams L2S are propagated along the corresponding lighting paths. The solid lines as shown in FIG. 2 denote some of the lighting paths, i.e. the transmission paths of the lighting beams (L2P+L2S).
After the source ray (L2P+L2S) provided by the illumination device 21 is transmitted through the collimating lens assembly 22 and directed to the reflective polarizer 23, the S-polarized lighting beams L2S are reflected to other places (not shown). The P-polarized lighting beams L2P are sequentially transmitted through the reflective polarizer 23 and the field lens 24, and directed to the LCOS microdisplay element 25. Next, the P-polarized lighting beams L2P are reflected by the LCOS microdisplay element 25. Correspondingly, the P-polarized lighting beams L2P are converted into a plurality of S-polarized imaging beams I2S in response to the electronic image. The S-polarized imaging beams I2S are propagated along the corresponding imaging paths. The dotted lines as shown in FIG. 2 denote some of the imaging paths, i.e. the transmission paths of the S-polarized imaging beams I2S.
The S-polarized imaging beams I2S from the LCOS microdisplay element 25 are transmitted through the field lens 24, and directed to the reflective polarizer 23. Next, the S-polarized imaging beams I2S are reflected by the reflective polarizer 23, and directed to the optical projection lens 26 through the analyzer 28. Consequently, the electronic image shown on the LCOS microdisplay element 25 is projected onto the screen 9 through the optical projection lens 26.
From the above discussions, the P-polarized lighting beams L2P are transmissible through the reflective polarizer 23, and the S-polarized imaging beams I2S are reflected by the reflective polarizer 23. However, the reflectivity and the transmissivity of the reflective polarizer 23 are not ideally 100%. In other words, a portion of the P-polarized lighting beams L2P incident to the reflective polarizer 23 are transmitted through the reflective polarizer 23 and directed to the LCOS microdisplay element 25. Whereas, the rest of the P-polarized lighting beams L2P are consumed or lost. In addition, a portion of the S-polarized imaging beams I2S incident to the reflective polarizer 23 are reflected by the reflective polarizer 23 and directed to the optical projection lens 26. Whereas, the rest of the S-polarized imaging beams I2S are consumed or lost. That is, the light amount outputted from the optical projection lens 26 is much lower than the light amount outputted from the illumination device 21.
From the above discussions, one of the main drawbacks of the conventional LCOS projection system is the low light utilization efficacy of the source ray provided by the illumination device. Consequently, the projection system outputs insufficient luminance and fails to meet the user's requirements. Recently, the LCOS projection system is gradually replaced by a digital light processing (DLP) projection system.
Therefore, there is a need of providing an improved LCOS projection system with enhanced light utilization efficacy.